Morgan
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LED Lights
Might this be of concern? I've read some flashlight warnings and some LED house bulbs are too bright without a lampshade, rather blinding to me.
http://www.livescience.com/31949-led-lights-eye-damage.html
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violet sin
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Not surprising, I got a good headache after testing some 3W UV LED's a while back. Obviously indirect viewing of the light(reflected), short (several
seconds) view time with eyes squinted, hurt none the less.Trying to leave accurate feedback on a new to me seller. The pain was anticipated though.
Problems from standard non UV lights would be surprising. Smething to look into, thanks
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zwt
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I'm not convinced the newest LED bulbs are any worse than incandescent bulbs or sunlight (fluorescent bulbs suck).
Which light bulb looks most like sunlight?
This video seems to contradict this claim from the article: "The light from LEDs, or light-emitting diodes, comes primarily from the short-wave,
high-energy blue and violet end of the visible light spectrum." The diode junction itself may generate "high-energy blue and violet" light, but that
doesn't mean it's what comes out of the bulb.
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Morgan
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Some other thoughts. I'm still cautious that some LED bulbs are too bright, such as hanging lights or those below ceiling fans without a shade if
you're in a relatively close proximity. The array of lights above a bathroom mirror comes to mind as well, they're right in your face.
"If you compare something like a frosted incandescent lamp, where the light is emitted from a large surface area, to an LED where the same amount of
energy is emitted from a tiny 1 square millimeter chip, the latter will be much brighter and will concentrate energy into a smaller spot when imaged
onto your retina."
"There is nothing particularly harmful about the light from LEDs though. If you use LEDs as a substitute for incandescent or fluorescent lamps for
indoor lighting, all else equal, it will be no better or worse for your eyes.*
https://www.quora.com/Is-indirect-LED-light-harmful-to-the-e...
This thought vaguely reminded me of tinnitus sufferers, how the sound, if you will, gets "burned" into the circuitry or maybe how phantom limb pain is
remembered?
"Excessive brightness is damaging even in the visible spectrum. It's not just direct UV damage of the retina, also the overstimulation of the receptor
cells can cause damage, due to many causes: depletion of cell's energy can cause harmful metabolic pathways. Excess of neurotransmitters can damage
neurons and surrounding tissue. Overloaded neurons can "burn" wrong responses into the circuitry."
http://physics.stackexchange.com/questions/158274/does-stari...
[Edited on 24-9-2016 by Morgan]
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careysub
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For reference the total surface emission (W/cm^2) for a tungsten filament is (2550 C) is 360 W/cm^2. A bare filament of course emits both infrared and
UV which can have separate adverse effects on the eye.
The very brightest LEDs are currently about 300 W/cm^2, but most are much less than this.
No IR or UV are emitted and they look brighter than their power output would indicate due to a better photopic spectrum.
The typical spectrum of the a white LED looks like this. The LED emits at about 450 nm, entirely in the visible spectrum, and excites a phosphor mix
that gives the broad hump at lower wavelengths.
[Edited on 25-9-2016 by careysub]
About that which we cannot speak, we must remain silent.
-Wittgenstein
Some things can never be spoken
Some things cannot be pronounced
That word does not exist in any language
It will never be uttered by a human mouth
- The Talking Heads
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zwt
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The spectra in the video I linked show a much smaller peak in the bluish part of the spectrum for both types of LED bulbs tested.
(here's the video again)
Why would the spectra in the video be so different from the one in the above post?
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careysub
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Quote: Originally posted by zwt  | The spectra in the video I linked show a much smaller peak in the bluish part of the spectrum for both types of LED bulbs tested.
(here's the video again)
Why would the spectra in the video be so different from the one in the above post? |
Different types of LEDs will have different specific curves, but they all have common features, the peak around 450 nm from direct LED emission, the
phosphor hump that gives the LED a white appearance, and the lack of any UV or IR emission. I posted the one above simply because it was in color
(useful for pedagogic reasons).
Every major LED maker publishes emission curves of their products, you should look up the specific one if you are interested. Warm white and cool
white are two common types with somewhat different curves.
I am not going to waste 7.5 minutes of my time watching a video. I hate videos, it is a very time-wasteful way of presenting information, unless the
subject actually benefits from watching the performance of some action.
[Edited on 25-9-2016 by careysub]
About that which we cannot speak, we must remain silent.
-Wittgenstein
Some things can never be spoken
Some things cannot be pronounced
That word does not exist in any language
It will never be uttered by a human mouth
- The Talking Heads
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zwt
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Thank you for answering my question. This is the spectrum of
one of the two LED bulbs he measured (the other was very similar), cropped from a screen shot.
[Edited on 25-9-2016 by zwt]
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Morgan
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The "cheap LED lightbulb from China" certainly blinks at 1000 fps.
https://www.youtube.com/watch?v=lwp9wAKzRtc#t=7m17s
Some tidbits about eyes to sift through, other views.
"You have likely heard that looking at a total eclipse can be dangerous. It indeed can be. And this is because the pupil responds to average light.
During a total eclipse, the pupil swells to its full size owing to the twilight's low average intensity. Its diameter swells to about 7mm7mm: so the
aperture has fifty times the area it has just before the eclipse begins. If you look at the diamond ring just after totality, you can therefore cop a
dose of 20mW20mW or so in the eye. This can be enough to cause thermal damage. Evolution didn't kit us out to look at total eclipses;
"Some eye conditions mean that even the thermal loading on the eye from the Sun can be dangerous. Macular degeneration is a major one, as is albinism
or even an extremely white complexion. Heart and circulatory diseases are others. Other diseases and defects mean that the pupil cannot respond to
high light levels. Many recreational drugs can dilate the pupils severely, particularly hallucinogens like LSD, psylosin or mescaline can lead to eye
damage in this way."
"Interestingly, if you begin with the assumption that the Sun's intensity into a fully shrunken pupil of someone staring straight at the Sun
represents a safe upper limit to power dose (in the absence of UV), then you come up with dose limits that pretty closely match the ISO60825 laser
safety standards for visible light."
"The last comment is particularly relevant to you. ISO60825 does NOT tell the difference between coherent and incoherent light. You tread an LED
exactly as you would a laser: if you apply ISO60825 and determine that the light dose from your LED is intrinsically safe (i.e. class 1), then this is
a sound indication, aside from in severe cases of the diseases I mention above. The other factor I haven't mentioned is the blink response, which is
also accounted for by ISO80625, but this sets levels for class 2 and class 3A, which are not intrinsically safe, but which are deemed to be low enough
that an accidental looking into the beam will not be harmful owing to the shielding afforded by a healthy blink response (assumed to limit the light
dose to 0.25 seconds). Again, drugs severely interfere with this reflex."
http://physics.stackexchange.com/questions/158274/does-stari...
Another aspect. This author interested in sleep however.
"We may have learned this in grade school, a perfect mix of the primary colors red, blue and green will make white. Existing red LEDs along with
Nakamura’s bright green and blue LEDs finally made this possible."
"Only that’s not how most white LEDs work. After years hovering just the other side of impossible, blue LEDs became more efficient than their red
and green grandparents. So most white LEDs are actually deep blue LEDs with Nakamura’s yellow-white phosphor coating. Yellow-white + blue =
white."
"But even though our eyes try to average it out, the strong blue spectral component remains. And that’s where the trouble comes from. It seems
that the human biological clock evolved around fire so isn’t as easily fooled by reddish-yellow incandescent lights."
"It is possible that by refining LED composition and control circuits, an efficient white LED will be invented which does make use of a warmer balance
of red, green and blue LEDs. LEDs are rugged, efficient, long-lasting and very bright but nearly every new technology has a hidden downside which
must be studied and balanced against the advantages. LEDs are no different."
http://www.greenprophet.com/2012/09/led-lights-health-hazard...
[Edited on 25-9-2016 by Morgan]
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Morgan
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Light-Induced Retinal Damage Using Different Light Sources, Protocols and Rat Strains Reveals LED Phototoxicity and similar articles to the right.
https://www.ncbi.nlm.nih.gov/labs/articles/27751961/
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Dr.Bob
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Making statements about LEDs use is like making statements about chemicals, way to broad a topic to make a useful statement. There are several
different ways to make white light from LEDs, different brands and types use one or more of them in different fixtures. Some use blue LEDs with
phosphors, some use three or more colored LEDs to generate a mix of color, some have variable color or brightness settings that are adjustable. You
can also buy a variety of warm/cold light colors from various vendors. I have even seen some that look like fluorescent fixtures, mostly using
reflected light, they look really good. But just as compact fluorescents have improved, gotten cheaper, and are now cheaper, good LEDs are now
readily available, cheaper, and in a variety of types and colors.
But if the light is too bright, you can get a lower wattage bulb or use a dimmer, if it flickers, then it might just be too cheap, most of the good
ones use a much longer duration phosphor. There is at least one new variation of incandescent bulb that uses a IR filter/reflector from MIT to
generate more light from less power, and last longer with less energy so maybe we will find a way to use that trick to go back to better bulbs.
news.mit.edu/2016/nanophotonic-incandescent-light-bulbs-0111
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Morgan
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Scientific American article on phontonic crystals
http://optoelectronics.eecs.berkeley.edu/eliy_SCIAM.pdf
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